There are known methods for coating, with a coating solution, a surface of a film serving as a base material. Examples of the methods encompass a spin coating method, a spray coating method, a bar coating method, and a gravure coating method. The gravure coating method is carried out by (i) immersing, in a coating solution, a gravure roll having a surface on which unevenness is provided and (ii) causing the gravure roll to come into contact with a base material, so that the base material is coated with the coating solution collected in recesses. The gravure coating method is used for, for example, a step of forming a heat-resistant layer on a porous film base material during the process of producing a heat-resistant separator for a battery.
Patent Literature 1 discloses a method of producing a laminated thermoplastic resin film under certain conditions. With the method, it is possible to prevent a continuous dot-like coating stripe flaw from occurring as a result of fine flaws being connected to each other, which fine flaws are (i) formed on a surface of a film after the surface is coated with a coating solution and (ii) each formed by a resin component spreading in the form of a lower part of a mountain from an aggregate of particles contained in the coating solution.